12/21/2010
Section 12.1
Section 12.1
Characteristics of Chemical Bonds
Characteristics of Chemical Bonds
Objectives
A. Types of Chemical Bonds
1. To learn about ionic and covalent bonds and explain
how they are formed
2. To learn a little about the metallic bond
3. To learn about the polar covalent bond
4. To understand the nature of bonds and their
relationship to electronegativity
5. To understand bond polarity and how it is related to
molecular polarity
• Bond – force that holds groups of atoms together and
makes them function as a unit. It always involves
valence electrons.
A salt (NaCl) crystal
Section 12.1
Section 12.1
Characteristics of Chemical Bonds
Characteristics of Chemical Bonds
A. Types of Chemical Bonds
A. Types of Chemical Bonds
Ionic Bonding
Covalent Bonding
(a)
(b)
• Ionic compound results when a metal transfers its valence
electrons to a nonmetal atom.
• A covalent bond results when electrons are shared by nuclei
of nonmetal atoms.
Section 12.1
Section 12.1
Characteristics of Chemical Bonds
Characteristics of Chemical Bonds
A. Types of Chemical Bonds
A. Types of Chemical Bonds
Metallic Bonding
• Metals are held together by nondirectional covalent
bonds [metallic bonds] (the electron sea model) among
the closely packed atoms
(Polar) Covalent Bonding
• A polar covalent bond results when electrons are shared
unequally by nuclei
– One atom attracts the electrons more than the other atom
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12/21/2010
Section 12.1
Section 12.1
Characteristics of Chemical Bonds
Characteristics of Chemical Bonds
B. Electronegativity
B. Electronegativity
• Electronegativity – the relative ability of an atom in a
molecule to attract shared electrons to itself
– Increases from left to right across a period
– Decreases down a group of representative elements
• The polarity of a bond depends on the difference
between the electronegativity values of the atoms
forming the bond
•
Covalent
Polar Covalent
Ionic
Section 12.1
Section 12.1
Characteristics of Chemical Bonds
Characteristics of Chemical Bonds
B. Electronegativity
C. Bond Polarity and Dipole Moments
• A dipole moment results when a polar molecule has a
center for positive charge separate from a center for
negative charge
Section 12.1
Section 12.1
Characteristics of Chemical Bonds
Characteristics of Chemical Bonds
C. Bond Polarity and Dipole Moments
C. Bond Polarity and Dipole Moments
• Water molecule dipole moment
• The polarity of water affects its properties
– Permits ionic compounds to dissolve in it
– Causes water to remain liquid at higher temperature
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